The engineering practice shows that, under the condition of large discharge and high head, the energy dissipation of the swirling vertical shaft encounters the following problems, that is, 1) excessive flow velocity in the vertical shaft increases the risks of cavitation and cavitation erosion on the wall surface; 2) due to the centrifugal force of water stream, it is difficult to perform aeration by using the conventional annular aeration ridge, the function of aeration and cavitation mitigation can not work.
Chinese patent application with publishing No. CN 101294377A provides a swirling vertical shaft provided with an aeration ridge. The aeration ridge is arranged on the wall surface of the lower middle section of the vertical shaft, and formed by gradually shrinking the vertical shaft connecting with the upper flat section of a flood discharging tunnel from the middle part to the lower middle part and then suddenly expanding the wall surface. Compared to the swirling vertical shaft provided with a conventional annular aeration ridge, although the aeration condition of the water stream can be improved to enable near-wall water layer at the lower reaches to become into aerated water streams and mitigate the damage of overflowing section at the lower middle part of the vertical shaft caused by cavitation erosion. However, the swirling vertical shaft of such a structure is only suitable for small discharge for the small volume of the cavity for containing air formed by suddenly expanding makes the amount of air aerated into the water stream small. Under the condition of large discharge and high head, it is difficult to fully aerate the water stream in the vertical shaft, the water stream in the vertical shaft cannot be discharged smoothly, and the concentration of the air mixed in the water stream cannot be increased effectively under the condition of large discharge and high head.